Melting furnace with movable current carrying leads for a consumable electrode

ABSTRACT

A melting furnace using consumable electrodes furnished with movable current supply leads and a sensitive device for continuously weighing the weight of the electrode and accordingly controlling the electrode feeding movement.

United States Patent [72] Inventors Helmut Scheidig Rossdorf; Alfred Hauff, Bruchkobel; Uwe Reimpell,

4 Bruchkobel, allot Germany [21] Appl. No. 6,995

[22] Filed Jan. 30, 1970 [45] Patented Oct. 19, 1971 [73] Assignee Leybold-I-leraeus-Verwaltung G.m.b.II.

Koln-Bayental, Germany [32] Priority Apr. 10, 1969 [33] Germany [54] MELTING FURNACE WITH MOVABLE CURRENT CARRYING LEADS FOR A CONSUMABLE ELECTRODE 5 Claims, 2 Drawing Figs.

[52] US. Cl 13/13, 13/14 [51] Int. Cl 1105b 7/12, F27d 1 1/ 10 [50] Field of Search 13/9, 12, 13, 14

[56] References Cited UNITED STATES PATENTS 3,179,734 4/1965 Rede1eta1........ 13/12 3,379,818 4/1968 Wynne 13/9 X Primary Examiner-Bernard A. Gilheany Assistant Examiner-Roy N. Envall, Jr. Attorney-Joseph F. Padlon ABSTRACT: A melting furnace using consumable electrodes furnished with movable current supply leads and a sensitive device for continuously weighing the weight of the electrode and accordingly controlling the electrode feeding movement.

PATENT 00m 19 mn SHEET 10F 2 /h, WW

CARRYING LEADS FOR A CONSUMABLE ELECTRODE I The invention'relates to a melting furnace for usewith consumable electrodes which are fed forwardly by a feeding device and supplied with current by means of movable leads, the feed rate being controlled by means of a device for continuously determining the electrode weight. The term melting furnace" as employed herein shall be understood to cover all furnaces in which a consumable block of more or less regular shape is consumed by melting by means of supplied electrical energy, the molten metal being subsequently consolidated in. a block or continuous body. It is not relevant to the invention whether melting occurs at atmospheric pressure or in a vacuum. The invention therefore relates both to electric arc vacuum furnaces and to furnaces for smelting metal under a slag layer.

The term continuous weighing is intended to cover all weighing methods useful for recording or control, that is, also individual weighings which are performed at stated intervals. The value determined by weighing may be used not only for feed control but also for programming the current, pressure and the like. It is often preferred to control a melting furnace in response to continuously determined weights because other data available for control purposes, such as electric arc voltage and current generally provide unreliable indications of the distance to be controlled between the electrode and the melt in electric arc furnaces. Thus, short circuits, splashing of the melt, gas eruptions and cavities in the charge may initiate adjustments of improper magnitude or even of the wrong direction.

In order to overcome these shortcomings, the continuous weighing and evaluation of the charge weights in regulating circuits or only for control purposes is of especial value. For example, determination of the decrease in the weight of the charge per unit time, that is, the determination of the differential, for control and regulation purposes results in great uniformity of the-melting process.

It is known, for example, from German Pat. No. 1,157,739 to arrange a pressure responsive resistor in a portion of the meltingapparatus loaded by the weight of the electrode, and to feed the electrical data so obtained to a control device for the meltingrate by way of an amplifier and a differentiating circuit. The output signal of the weight indicator, however, is useful only if the weight is determined with great precision. However, the weight data are rendered inaccurate in all known melting'fumaces by the weight of the supply cable if the consumable electrode is supplied with current by a movable lead such as the cable. The cable, which is of great weight because of the heavy currents necessary, usually extends from a stationary terminal in a U-shaped, depending loop to the feed mechanism which travels downward with the electrode while the latter is being consumed. The length ratio between the portions of the cable whose weights are supported respectively by the stationary terminal and by the movable feed mechanism thus varies. As the length ratio varies, the loading of the two supporting elements by the cable also changes. If one were to use the'forces acting on the feed mechanism for the consumable electrode or on its drive for determining the electrode weight, the result of the weighing would .be different depending on the position of the feed mechanism and on the varying sag of the current carrying cable.

In order to avoid the shortcomings of the known devices, it is proposed according to the invention that the feed mechanism and the consumable electrode suspended from the same-rest on a platform which is supported on at least one weight indicating device, and one end of the movable current lead be connected with the consumable electrode by way of the feed mechanism, and the other end with the platform, the end of the movable lead attached to the platform being connected to a source of current by means of a flexible currentcarrying band. The term platform" is not intended to define the structuralfeatures or the geometrical shape of an element of the apparatus, but is to set forth that the element defines a reference plane in which all essential forces not due to the weight of the electrode and the constant weight of the drive mechanism are in equilibrium. The term movable current leads" is to cover all conductors which permit transmission of current to movable furnace elements, and at least partly move with the moving element. It is customary for this purpose to employ current-carrying cables or bands.

The arrangement of the invention has the following advantages:

It permits the weight signal generating device or devices to be arranged outside the zone of thermal influence of the furnace and'of the current path so that commercially available signal generating devices may be employed. In the case of a vacuum furnace, there is no need for a vacuum-tight leadthrough for the electrical connections of the signal generating device. Differences in the weights of the several legs of the movable current lead or the current cable are compensated as will be described hereunder, and cannot influence the measured values nor the control process. Because the actual weight of the electrode is determined exclusively, it is possible adequately to control the melting process, for example, by determining a difference as compared to a nominal value of the weight. The indicating devices are not exposed to damage by mechanical forces because forces other than those to be measured are without efi'ect or are safely intercepted. The feed mechanism, the platform, and the current-carrying cable thus constitute a closed system of forces. Only the weights of the charge, of the feed mechanism with drive, of the latform and of supplemental guides and linkages are effective from the outside and are received by the weight signal generating.

devices in a vertical direction. The weights of all these elements are known and constant, and can therefore be eliminated by suitable circuitry including balancing potentiometers or mechanically, for example, by counterweights.

It is not necessary to arrange the drive motor and the transmission for the forward feed on the platform, but driving energy can also be transmitted from an external motor to the platform, for example, by a Cardan shaft or a telescoping shaft. A particularly simple and compact arrangement is obtained if the platform additionally receives the drive or even serves as a housing for the drive of the feed mechanism.

Embodiments of the invention will be described hereinafter by reference to FIGS. l and 2 which show sectional views of two different variants of the same principle.

In FIG. 1, there are provided an interior chamber I of a vacuum furnace, and a furnace shell 2. Three signal generating devices or load cells 3 are provided for weight measurement which are measuring cans strain gages abut against the furnace housing. The load cell as known in the art is a strain sensitive means such as a wire, the electrical resistance of which is dependent on the strain pulling at the wire, or a piezocrystal which produces an electrical discharge under pressure, resulting in an electrical signal. The signal itself or the derivation of such a signal may be used for measuring or control purposes. Loadingthe measuring cans causes an increase in the electrical resistance which provides an input signal for the control or regulating process. A platform 4 rests on the devices 3 and functions as a weighing platform. A force transmitting element constituted by two guide columns 5,6 extends upward from the platfonn. Two guide sleeves 7,8 are longitudinally movable on the columns and are connected by a transverse member 9.

The upper ends of the guide columns are fixedly connected with a drive housing 10 which encloses the motor and transmission for moving the furnace charge. These elements have not been shown in the drawing for the sake of simplicity. The drive mechanism causes a threaded spindle II to rotate, the spindle cooperating with a nut 12 and causing the feed mechanism 13 to be raised or lowered when the spindle turns toward the left or right, such as a moving screw. Because the nut I2 is connected with the transverse member 9, the guide sleeves 7,8 participate in the movement. The nut 12 is a ball box and constitutes the upper end of the feedmechanism 13 whose lower end, not shown in the drawing, is equipped for holding the charge. The feed mechanism passes through the furnace wall at 14, a seal 15 being provided to maintain the vacuum in the chamber 1 of the furnace, and permitting sliddirectly with the platform 4. Acompensating member 18 balances the forces generated by the cross section and the pressure difference at the intermediate bellows member 16. Pressure equalization is achieved by the line 19 which communicates with the interior chamber '1 of the furnace.

Lateral displacement of the platform 4 is prevented by two guide pins 20 mounted on the platform and capable of sliding practically without friction in pin bearings 21. This arrangement, however, may also be replaced by a known assembly of horizontal linkages with equally good results. An angularly offset bus bar 23 is fixedly mounted on the platform 4 on a plate 22 of insulating material. One end 25 of the movable current lead constituted by a current-carrying cable 26 is fastened to one projecting leg 24 of the bar 23. The other end 27 of the cable 26 is fastened to the free end of an arm 28 which serves as a current lead to the movable feed mechanism 13. The arm is conductively connected with the nut 12 of the feed mechanism 13 and moves up and down with the same. The other end 29 of the bar 23 receives the flexible currentcarrying band 30 whose opposite end is connected with a terminal 31 conductively connected to a current source. The terminal 31 is attached to a building portion 32 in the instant embodiment.

The apparatus shown in FIG. 1 operates as follows:

Each of the two ends 25,27 of the cable 26 transmits its weight portion of the cable to the bar 23 and the arm 28 a respectively, the transmitted portion of the weight of the cable corresponding substantially to the length ratio from the lowest point 33 to the respective end of the cable portion. The weight portion of the end 25 directly loads the platform 4 in the direction of the arrow 34, and thus loads the weight-indicating signal generating device 3. The weight portion of the weight end 27 at first loads the feed mechanism 13 in the direction of the arrow 35. A reaction force together with other forces of the system is transmitted by way of the threaded spindle 11 in the direction of the arrow 36 to the drive housing and from there to the guide columns 5,6 in the direction of the arrows 37,38. The forces are further transmitted by the columns 5,6 to the platform 4, and thus to the signal generating device 3. It is evident that the signal generators 3 are acted upon at all times by the sum of the forces on the two cable ends 25,27. The forces acting on the signal generators are therefore independent from the instantaneous position or the sag of the cable 26. v

Frictional forces generated by movement of the feed mechanism 13 in the seal and by the movement of the guide sleeves 7,8 on the columns 5,6 are balanced completely relative to the platform 4 and the signal generators 3 because the feed mechanism 13 forms a closed system of forces jointly with the threaded spindle 11, the drive housing 10, the guide columns 5,6 and the platform 4. The signal generators 3 are thus loaded only with the constant weights of the feed mechanism and of its drive, the guide columns, and the platform, as well as auxiliary guiding elements and linkages, and of the current supply leads with their fastening elements, and also with the variable weight of the charge which is to be determined. The weight changes of the charge cause the signal generators 3 to undergo a length change of a few tenths of a millimeter, and the platform must follow accordingly. However, the resulting deformations of the resilient current-carrying band 30 and of the resilient intermediate bellows member 16 are so small as not to cause measurable reaction forces to be transmitted to the platform.

Instead of the stationary mounting of the terminal 31 for the end of the band 30 remote from the furnace, one may provide the terminal 31 with another movable current-carrying lead which sags in a downward loop. This permits the entire furnace top together with the feed mechanism 13 and its drive and the cable 26 to be shifted vertically and horizontally for replenishing the charge. In this event, the terminal 31 is connected with the furnace housing 2 which is not covered by the weighing or with a frame 39 (FIG. 2).

FIG. 2 shows a modification of the apparatus of FIG. 1. The

furnace housing has an upwardly extending, closed frame 39 which encloses the superposed drive housing 10 and the feed mechanism 13. The frame has two supported arms 40 which support two signal generators 3. The platform 4 and drive housing 10 constitute a unitary structure secured against lateral shifting by the guide pin 41 and the pin bearing 42. The drive and linear guide arrangement for the feed mechanism 13 are identical with the embodiment of FIG. L-The seal 15 is fastened in a yoke or bridge 43 which transmits the frictional forces to the guide columns 5,6 and from there to the platform 4 and thereby closes the system of forces. Contrary to the apparatus of FIG. 1, the columns 5,6 are relieved of the weight of the charge and of the drive.

The platform 44 is extended laterally by a bracket 44 which is guided freely movably past the frame 39. The bus bar 23 is located on the bracket 44 being provided with a plate 22 of insulating material by analogy with FIG. 1. The bar 23 is connected with the flexible current-carrying band 30 and also with the end 25 of the cable 26. The other end 27 of the cable is fastened to a carrying arm 28 which is either guided laterally past the frame 39 and the guide column 5 or encloses these elements in freely movable relationship. The electrical connection to the carrying arm is provided at the nut 12 of the feed mechanism 13. Lateral movement of the bridge 43 is prevented by the guide pin 20 and the pin bearing 21 or by the analogous linkage arrangement. As to the mobility of the terminal 31 by means of an additional movable current-carrying load, current-carrying above statement relating to FIG. I is applicable.

What is claimed is:

l. A melting furnace for use with consumable electrodes supplied with current by movable current supply leads and provided with a device for continuously weighing the weight of the electrode and for accordingly controlling the electrode feeding movement, comprising a feed mechanism, a consumable electrode suspended from said mechanism, a platform for said electrode, said platform being supported on at least one that said terminal is in connection with the furnace which is not weighed, and is connected with a stationary terminal by an additional movable current-carrying lead.

' 3. A melting furnace according to claim 1, characterized in that said terminal is in connection with a frame therefor which is not weighed, and is connected with a stationary terminal by an additional movable current-carrying lead.

4. A melting furnace according to claim 1, wherein said platform additionally serves for receiving the drive for said feed mechanism.

5. A melting furnace as set forth in claim 1, wherein said platform is provided with at least two guide means to prevent lateral displacement thereof. 

1. A melting furnace for use with consumable electrodes supplied with current by movable current supply leads and provided with a device for continuously weighIng the weight of the electrode and for accordingly controlling the electrode feeding movement, comprising a feed mechanism, a consumable electrode suspended from said mechanism, a platform for said electrode, said platform being supported on at least one weight signal generator, and a movable current-carrying lead connected with the consumable electrode by said feed mechanism, and also with said platform, the end of said movable current-carrying lead engaging said platform and connected with a terminal of a current source by means of a flexible current-carrying band.
 2. A melting furnace according to claim 1, characterized in that said terminal is in connection with the furnace which is not weighed, and is connected with a stationary terminal by an additional movable current-carrying lead.
 3. A melting furnace according to claim 1, characterized in that said terminal is in connection with a frame therefor which is not weighed, and is connected with a stationary terminal by an additional movable current-carrying lead.
 4. A melting furnace according to claim 1, wherein said platform additionally serves for receiving the drive for said feed mechanism.
 5. A melting furnace as set forth in claim 1, wherein said platform is provided with at least two guide means to prevent lateral displacement thereof. 